What’s the Difference Between a Vulnerability Scan and a Penetration Test?

When businesses start to take cyber security seriously, two terms often come up: vulnerability scanning and penetration testing. They’re sometimes used interchangeably, but in practice, they serve very different purposes.

Both help you identify weaknesses in your IT systems and reduce your risk of attack. But they do it in different ways, and they provide different types of insight. To make informed decisions about where to focus your security efforts, and budget, it’s important to understand how each one works.

What is a Vulnerability Scan?

A vulnerability scan is an automated process that checks your systems for known weaknesses. Think of it as a regular health check: it looks for missing patches, outdated software, misconfigured services, and other common security issues that are already known to attackers.

Scans typically reference databases of known vulnerabilities (such as CVEs) and compare them to your systems and software. This means they’re fast, repeatable, and ideal for identifying technical gaps that could be exploited if left unaddressed.

You can run vulnerability scans internally or externally:

• Internal scans focus on devices and systems inside your network (like employee laptops and servers).
• External scans look at what can be seen and potentially exploited from the internet, such as your website or remote access points.

Because they’re automated, scans are relatively low-cost and are often scheduled to run weekly, monthly, or quarterly. For businesses working towards Cyber Essentials Plus, regular vulnerability scanning is a requirement.

What is a Penetration Test?

A penetration test (or pen test) is a much more in-depth exercise. It involves a CREST qualified tester simulating a real-world attack against your systems, using the same techniques as malicious hackers but in a controlled and authorised way.

Where a vulnerability scan might flag a known software weakness, a penetration tester will take it further. They’ll see if it can be exploited, what kind of access it grants, and what damage a real attacker might do if they got in.

For example, a pen tester might:

• Chain multiple vulnerabilities together to move through your network
• Exploit a weak password policy to access admin accounts
• Use social engineering tactics to test how staff respond to phishing emails

Penetration tests are often scoped to cover specific areas, such as web applications, internal networks, or cloud environments. They provide far richer insight than a scan alone, but they also require more time, budget, and planning.

Key Differences at a Glance

The key differences between a vulnerability scan and a penetration test come down to method, depth, purpose, and frequency.

A vulnerability scan is automated, broad in scope, and designed to identify known issues quickly. It’s typically low cost and well-suited to regular use, for example, monthly or quarterly. The output is a list of vulnerabilities, which can then be prioritised and addressed internally.

In contrast, a penetration test is typically manual and far more in-depth. It involves a skilled ethical hacker simulating a real-world attack to see how far they can get. This process is more time-intensive and higher cost, but the result is a detailed report showing the impact of any weaknesses discovered, not just that they exist. Penetration tests are often carried out once a year, or after significant system changes, and are commonly required for businesses handling sensitive data or pursuing advanced cyber certifications.

Both play a valuable role. One helps you maintain awareness of surface-level risks, while the other shows what could happen if those risks are exploited.

Which One Do You Need?

The short answer is: both, but not necessarily at the same time.

Here’s how many of our clients at Formentor approach it:

• Start with a vulnerability scan to get a baseline of known risks and quick wins.
• Use the results to patch gaps and strengthen your defences.
• Then run a penetration test to explore how far an attacker could get, based on your actual setup and user behaviour.

Vulnerability scans are great for ongoing monitoring and continuous improvement. Penetration tests provide assurance that your controls hold up under pressure.

If you’ve never done either, a scan is a good first step. If you’ve done the basics and want to go deeper, or need to meet the expectations of insurers, investors, or public sector clients, a pen test adds another level of rigour.

Where These Fit in Compliance

If you’re working towards:

• Cyber Essentials Plus, you’ll need a vulnerability scan as part of the assessment.
• ISO 27001, penetration testing can support your risk assessment process and help evaluate technical controls.
• Client contracts or frameworks, you may be asked for evidence of both, especially if you handle sensitive or regulated data.

A Practical Approach

Cyber security isn’t one-size-fits-all, and it doesn’t have to be overwhelming. At Formentor, we work with businesses of all sizes to help them understand where they are today, where the risks are, and what testing approach makes sense.

Some clients start with a Cyber Security Assessment. Others come to us needing help preparing for certification or responding to a specific client demand. Wherever you’re starting from, we can help you build the right testing and improvement roadmap.

Not sure whether you need a vulnerability scan, a penetration test, or both?
We’ll help you figure it out, based on your goals, systems, and risk profile.